The invention relates to a voltage regulator, such as a switching voltage regulator.
A DC-to-DC voltage regulator typically is used to convert a DC input voltage to either a higher or a lower DC output voltage. One type of voltage regulator is a switching regulator which is often chosen due to its small size and efficiency. The switching regulator typically includes one or more switches that are rapidly opened and closed to transfer energy between an inductor (a stand-alone inductor or a transformer, as examples) and an input voltage source in a manner that regulates an output voltage.
As an example, referring to FIG. 1, one type of switching regulator is a synchronous Buck switching regulator 10 that receives an input DC voltage (called V.sub.IN) from an input voltage source 9 and converts the V.sub.IN voltage to a lower regulated output voltage (called V.sub.OUT) that appears at an output terminal 11. To accomplish this, the regulator 10 may include a switch 20 (a metal-oxide-semiconductor field-effect-transistor (MOSFET), for example) that is operated (via a switching control voltage called V.sub.SWITCH1) by a controller 15 in a manner to regulate the V.sub.OUT voltage.
Referring also to FIGS. 2 and 3, in particular, the controller 15 opens and closes the switch 20 to control energization/de-energization cycles 19 (each having a constant duration called T.sub.S) of an inductor 14. In each cycle 19, the controller 15 asserts (drives high, for example) the V.sub.SWITCH1 voltage during an on interval (called T.sub.ON) to Close the switch 20 and transfer energy from the input voltage source 9 to the inductor 14. During the T.sub.ON interval, a current (called I.sub.L (see FIG. 3)) of the inductor 14 has a positive slope. During an off interval (called T.sub.OFF) of the cycle 19, the controller 15 deasserts (drives low, for example) the V.sub.SWITCH1 voltage to open the switch 20 and isolate the input voltage source 9 from the inductor 14. At this point, the level of the I.sub.L current is not abruptly halted, but rather, a diode 18 (see FIG. 1) begins conducting to transfer energy from the inductor 14 to a bulk capacitor 16 and a load (not shown) that are coupled to the output terminal 11. During the T.sub.OFF interval, the I.sub.L current has a negative slope, and the controller 15 may close another switch 21 (via a signal called V.sub.SWITCH2) to shunt the diode 18 to reduce the amount of power that is otherwise dissipated by the diode 18. The bulk capacitor 16 serves as a stored energy source that is depleted by the load, and additional energy is transferred from the inductor 14 to the bulk capacitor 16 during each T.sub.ON interval.
For the Buck switching regulator, the ratio of the T.sub.ON interval to the T.sub.OFF interval, called a duty cycle, generally governs the ratio of the V.sub.OUT to the V.sub.IN voltages. Thus, to increase the V.sub.OUT voltage, the controller 15 may increase the duty cycle, and to decrease the V.sub.OUT voltage, the controller 15 may decrease the duty cycle. For purposes of monitoring the V.sub.OUT voltage, the controller 15 may receive a voltage (called V.sub.P) that is proportional to the V.sub.OUT voltage. The V.sub.P voltage may be provided by a resistor divider 13 that is coupled to the output terminal 11.
The regulator 10 may be used in a computer (a laptop computer, for example) that is capable of entering a power conservation mode, such as a stop clock mode, for example. In the power conservation mode, the power losses introduced by the on-off transitions of the switches 20 and 21 become significant, as compared to the total amount of power being consumed by the computer. Therefore, for purposes of maximizing the efficiency of the regulator 10, the controller 15 may leave the switch 21 open during the power conservation mode.